Four color digital cinema system with extended color gamut and copy protection

ABSTRACT

A color display system including a display device for four or more visible color primaries and a processor for controlling the four or more color primaries to selectively render portions of an image or image sequence such that visually equivalent colors displayed in two or more image portions differ in their spectral composition.

FIELD OF THE INVENTION

This invention generally relates to a display apparatus for embeddinginformation in an image and more particularly relates to a method formarking and distorting a displayed image (e.g., a displayed motionpicture image) in order to discourage recording the image with a videocamera.

BACKGROUND OF THE INVENTION

Movie piracy is a cause of substantial revenue loss to the motionpicture industry. Illegally copied movies, filmed during projection withvideo cameras or camcorders and similar devices, are a significantcontributing factor to revenue loss. Even the questionable quality ofmovies pirated in this fashion does not prevent them from broaddistribution in the “black market”, especially in some overseas markets,and on the Internet. As video cameras improve in imaging quality andbecome smaller and more capable, the threat of illegal copying activitybecomes more menacing to motion picture providers. While it may not bepossible to completely eliminate theft by copying, it can beadvantageous to provide display delivery techniques that frustrateanyone who attempts to copy a motion picture using a portable videocamera device. While this is a highly visible problem in the motionpicture industry, this same problem is likely to be manifested in otherindustries that use digital media.

Skilled practitioners know how to provide a distinct symbol or watermarkto an original still image as a means of image or copy identification,such as in order to authenticate a copy. U.S. Pat. No. 5,875,249(Mintzer et al.), U.S. Pat. No. 6,031,914 (Tewfik et al.), and U.S. Pat.No. 5,912,972 (Barton) disclose methods of applying a perceptuallyinvisible watermark to image data as verification of authorship or asevidence that an image has not been altered. Although, such methodsidentify and validate image data, they provide no direct means ofprotection against copying an image, for example, with a conventionalscanner and color printer. In contrast, U.S. Pat. No. 5,530,759(Braudaway et al.) discloses providing a visible, color correctwatermark that is generated by altering brightness characteristics, butnot chromaticity of specific pixels in the image. Yet the approach usedin U.S. Pat. No. 5,530,759 could be objectionable, if used for a motionpicture, since the persistence of an image or a mark overlaid on themoving image could annoy an audience and adversely affect the viewingexperience.

The above examples for still images illustrate a key problem: aninvisible watermark identifies but does not adversely affect the qualityof an illegal copy, while a visible watermark can be distracting andannoying. With video and motion picture images, that include multipleimages, there can be yet other problems with conventional imagewatermarking. For example, U.S. Pat. No. 5,960,081 (Vynne et al.)discloses applying a hidden watermark to MPEG data using motion vectordata; but this method identifies and authenticates the originalcompressed data stream and would not provide identification for a motionpicture that was copied using a camcorder. Other patents, such as U.S.Pat. No. 5,809,139 (Girod et al.), U.S. Pat. No. 6,069,914 (Cox), andU.S. Pat. No. 6,037,984 (Isnardi et al.) discuss adding an imperceptiblewatermark directly to the discrete cosine transform (DCT) coefficientsof an MPEG-compressed video signal. These methods, however, provide awatermark that is primarily detectable in the compressed image dataitself. When watermarked images are subsequently recompressed, using alossy compression method, (with a camcorder, for example) or aremodified by some other image processing operation, the watermark may nolonger be detectable.

The watermarking schemes disclosed in the patents listed above add awatermark to the compressed bit stream of an image or image sequence.Alternatively, there are other watermarking schemes that add thewatermark to the image data itself, rather than to the compressed datarepresentation. An example of such a scheme is given in U.S. Pat. No.6,044,156 (Honsinger et al.), which discloses a spread spectrumtechnique using a random phase carrier. However, regardless of thespecific method that is used to embed a watermark, there is always adesire that a watermarking method be robust; that is, able to withstandvarious “attacks” meant to remove or alter the watermark. Some attacksmay be deliberately aimed at the underlying structure of a givenwatermarking scheme and require detailed knowledge of watermarkingtechniques applied. However, most attack methods are less sophisticated,performing common modifications to the image such as using lossycompression, introducing low-pass filtering, or cropping the image, forexample. Such modifications can be made when a video camera is used tocapture a displayed motion picture. These methods present a constantthreat that a watermark may be removed during the recording process.

The watermarking schemes noted above are directed to copyidentification, ownership, or authentication. However, even if awatermarking approach is robust, provides copy control management, andsucceeds in identifying the source of a motion picture, an invisiblewatermark may not be a sufficient deterrent for illegal copying.

As an alternative to watermarking, some copy deterrent schemes used intechnologies other than video or movie display operate by modifying asignal or inserting a different signal to degrade the quality of illegalcopies. The modified or inserted signal does not affect playback of alegally obtained manufactured copy, but adversely impacts the quality ofan illegally produced copy. As an example of this principle, U.S. Pat.No. 4,644,422 (Bedini) discloses adding a degrading signal to discouragecopying of audio recordings. An audio signal having a frequency at andabove the high threshold frequency range for human hearing isselectively inserted into a recording. The inserted signal is notdetectable to the listener. However, any unauthorized attempt to copythe recording onto tape obtains a degraded copy, since the insertedaudio signal interacts adversely with the bias oscillator frequency of atape recording head.

As a variation of the general method where a signal is inserted thatdoes not impact viewability, but degrades copy quality, U.S. Pat. No.6,018,374 (Wrobleski) discloses the use of a second projector in videoand motion picture presentation. This second projector is used toproject an infrared (IR) message onto the display screen, where theinfrared message can contain, for example, a date/time stamp, theateridentifying text, or other information. The infrared message is notvisible to the human eye. However, because a video camera has broaderspectral sensitivity that includes the IR range, the message will beclearly visible in any video camera copy made from the display screen.The same technique can be used to distort a recorded image with an“overlaid” infrared image. While the method disclosed in U.S. Pat. No.6,018,374 can be effective for frustrating casual camcorder recording,the method has some drawbacks; including the fact that the pattern isfixed in space and, therefore, it is a relatively simple procedure toedit it from the digital data.

A more sophisticated video camera operator could minimize the effect ofa projected infrared watermark by placing a filter designed to blockinfrared light in the video camera's optical path. A further drawback ofthe method is that a fourth image channel, an additional projector, ormodifications to the projection screen is required to implement thismethod, and this additional hardware can add significant cost to adisplay or projection system without providing any benefit beyonddefeating movie piracy.

While display systems typically provide for three color channels for thedisplay of visible light, it is also known in the art to provide displaysystems which project four or more channels of visible light to enhancethe viewing experience. These display systems can provide additionalcolor primaries to expand the color gamut of the display system asdescribed by U.S. Pat. No. 6,570,584 (Cok et al.) or to increase thebrightness of the display system as described by U.S. Pat. No. 5,233,385(Sampsell).

There remains a need for a method and a display system that allowswatermarking and copy-deterrent marking of image content (e.g., motionpicture content), that utilizes visible light, and yet allows thewatermark information to be displayed such that it is invisible to theviewer, yet quite apparent in an illegal video copy.

SUMMARY OF THE INVENTION

The aforementioned need is met according to the present invention byproviding a color display system, comprising:

(a) a display device having four or more visible color primaries capableof producing metamerically matched color stimuli; and

(b) a processor for controlling the four or more color primaries toselectively render portions of an image or image sequence such thatvisually equivalent colors displayed in two or more image portionsdiffer in their spectral composition.

Another aspect of the invention provides a method for a method for usingvisible light to deter unwanted copying of image content, comprising thesteps of;

(a) combining four or more visible color primaries to render differentportions of an image or image sequence such that a given input imagecolor displayed in two or more portions has a different spectralcomposition and is perceived as visually equivalent; and

(b) displaying the portions as part of the image content.

Still another aspect of the invention provides a method for a method forhiding and revealing text or image data using a display device,comprising the steps of:

(a) combining four or more visible color primaries to render portions ofan image or image sequence such that visually equivalent colorsdisplayed in two or more image portions differ in their spectralcomposition; and

(b) providing a means for visually differentiating the portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a CIE chromaticity prior art diagram showing coordinates forred, green, blue and cyan color primaries.

FIG. 2 is a schematic diagram showing the system components of oneembodiment that are useful to practice the present invention.

FIG. 3 is a flow chart illustrating an exemplary process for renderinginformation to a display device to practice the present invention.

FIG. 4 a flow chart illustrating an exemplary process for forming a setof conversion methods useful in converting an input image to an imageuseful in the present invention.

FIG. 5 is a flow chart illustrating an exemplary process for applyingthe input-image conversion.

FIG. 6 is a graph showing the spectral location and emission of a set ofdisplay primaries useful in practicing the present invention.

FIG. 7 is a graph showing the spectral response for a typicalimage-recording device that might be used to record an image from adisplay device of the present invention;

FIG. 8 is a graph showing the print-through grayscale characteristic ofa typical image-recording device that might be used to record an imagefrom a display device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present description is directed in particular to elements formingpart of, or cooperating more directly with, apparatus in accordance withthe invention. It is to be understood that elements not specificallyshown or described may take various forms well known to those skilled inthe art.

In the description and claims that follow, the term “invisible” or“substantially invisible” uses the conventional meaning, that is, notperceptible to the unaided human eye. In the context of the presentinvention, it will be understood that visual content that is intended tobe invisible may be near or slightly above detectability limits for someobservers. Similarly, the term “visually equivalent” describes multiplestimuli that appear the same to a normal human observer. In the contextof the present invention, it will be understood that content that isintended to be visually equivalent may be near or slightly abovedetectability limits for some observers. Further, the term“metamerically matched” refers to color stimuli that are visuallyequivalent, as defined above, therefore the color difference betweenmetamerically matched stimuli may be near or slightly abovedetectability limits for some observers.

It is understood that the neural signals that enable human visionoriginate in the human retina. It is further understood that the sensorsthat are present in the human retina and that result in photopic (i.e.,daylight) vision are of one of three types with one of three spectralsensitivities. As a result, the three retinal responses resulting fromany visible color stimulus that is viewed under photopic conditions canalso be synthesized from a combination of three color primaries whosechromaticities enclose those of the color stimulus when the colorstimulus and the primaries are plotted in the 1931 CIE chromaticitydiagram. The human visual system also includes a fourth type of sensorwith a fourth spectral sensitivity. However, this sensor is active onlyunder low-light conditions.

For the present invention, the fact that the human visual system hasthree active sensors under normal photopic viewing conditions means thata combination of any three distinct color primaries may be used to formany color stimulus whose chromaticities are within the triangle formedby the color primaries' chromaticity coordinates when plotted in the1931 CIE chromaticity prior art diagram as shown in FIG. 1. FIG. 1 showsthe chromaticity coordinates of a set of red 2, green 4, and blue 6color display primaries. While these three color primaries arerepresentative of those used within traditional display devices, anythree color primaries within the 1931 CIE chromaticity diagram spectrumlocus may be applied within this invention. A color gamut boundary 8 maybe drawn within the 1931 CIE chromaticity space by connecting thechromaticities of the three color primaries, thus forming a triangle.

A color whose chromaticities are contained within the color gamutboundary 8 may be formed using a linear combination of the red 2, green4, and blue 6 primaries. A fourth color primary having a fourthchromaticity coordinate 10 also may be incorporated in the displaydevice. In this example, the color of the fourth color primary may bedescribed generally as cyan, however, any other additional color primaryalso may be applied within this invention. Examining FIG. 1 further, onecan see that once this fourth color primary's chromaticity coordinatesare added to the 1931 CIE chromaticity diagram, two additional trianglesmay be drawn that overlap the initial triangle 8. These include atriangle that connects the red 2, green 4, and the fourth color primary10 chromaticity coordinates as well as the triangle that connects theblue 6, red 2, and the fourth color primary 10 chromaticity coordinates.Note that any color whose chromaticities fall within the color gamutboundary 8 may now be formed using either a linear combination of theoriginal red 2, green 4, and blue 6 primaries or by a linear combinationof two of the red 2, green 4, and blue 6 primaries in combination withthe fourth color primary 10. Further, any color whose chromaticities arewithin the color gamut boundary 8 can be formed from any linearcombination of these two solutions using all four color primaries.Therefore, a given color may be formed using any of a large number ofcolor-primary combinations.

One should note that the spectral composition of the light generated byany of these equivalent solutions will differ. Furthermore, while thehuman eye will perceive any of the linear combination solutions usingthe four primaries to be visually equivalent, the spectra produced bythese different solutions will each be captured differently by animage-capture device, such as a digital camera or camcorder. It is verydifficult, if not practically impossible, to design an image capturedevice that has spectral sensitivities corresponding to those of thehuman eye or any linear combination thereof. Instead, image-capturedevices generally are designed to have spectral sensitivities thatcoincide generally with the long (red), medium (green), and short (blue)wavelength regions of the visible spectrum, with the result that thesedevices will often detect colors differently than they are detected bythe human visual system. This fact is demonstrated within the examplecalculations that are provided within this disclosure.

The principle of the present invention is the selective rendering ofdifferent portions of an image or image sequence using a display devicehaving four or more color primaries. Herein, rendering is defined as theprocess of producing a light output having a desired color spectrum orthat is defined in a known coordinate color space. The display devicemay render a specific spatial portion of an image or temporal portion ofan image sequence using one linear combination of the four or moreprimaries and render one or more other portions of said image or imagesequence using one or more additional linear combinations of the fourprimaries. The linear combinations of primaries produce light outputwith substantially consistent chromaticity coordinates and luminance,but that differ in their spectral composition. The portions may beselected to form an image or text watermark. The watermark, for example,may provide information about the copyright of the image content, theowner or location of the display device or any other relevantinformation. Since the unaided human eye will perceive color stimuliproduced in different image portions by different combinations of the atleast four color primaries as being visually equivalent, the differentportions will appear homogenous to the unaided eye of the observer.However, when such an image is recorded using an image-capture device,color stimuli produced in the different spatial regions by differentcombinations of the at least four color primaries will be recordedinconsistently and/or non-uniformly, making the spatial regions, i.e.,the watermark, visible in any reproduction created from said recording.Since digital images collected by an image-capture device may be editedto correct the color within the different spatial regions, this editingprocess may be essentially defeated by random location selection of thespatial regions or by varying the spatial regions temporally.Alternatively, or in combination, image areas having a high degree ofspatial detail may be selected for alternate color primary rendering;thus, making it difficult to edit the digital content of reproductionscreated from said device recordings. The selection of image portionswith high spatial detail may also make it difficult to see any nearthreshold changes in color that may be present in the final renderedimage.

In a motion image sequence, the linear combinations of the colorprimaries may also vary between different image frames. Temporallychanging the rendering of one or more image portions makes editingimages collected by an image-capture device extremely difficult. Aportion may be altered within an image sequence on a frame-by-framebasis, or rendering values may also be randomly or semi-randomlyselected to make this difference less predictable. Alternatively,different spatial portions within the motion image sequence may beselected as a function of time. Using this method, an observer directlyviewing the original display image should once again see no visualdegradation, while an observer viewing a reproduction of a capture ofthe image or image sequence should see significant changes in the colorof some regions within the image over time.

Alternatively, particular critical colors, such as those correspondingto human skin tones, may be selected and a linear combination of colorprimaries may be applied to these critical colors different from thelinear combination of color primaries applied to other colors within animage frame. This may be accomplished by clustering the image pixelcolors within a scene, expressed in terms of a uniform color space, suchas CIELAB, and applying a color-primary rendering to the image pixels ina particular color cluster different from the color-primary renderingapplied to the remaining pixels in the scene. This rendering also may bechanged on a scene by scene basis. Because an observer viewing aprojected or self-luminous reproduction of a recording of a displayedimage created by applying the teachings of the present invention should,to a large degree, visually adapt to the average color of the majorityof the image, the image areas corresponding to the selected colorclusters appear as either incorrect (e.g., greenish skin tones) orchanging from frame to frame. This effect will degrade the visualquality of any reproduction created from captures of images created bythe display device of the present invention using an image-capturedevice.

Referring to FIG. 2, a system employing the present invention willtypically be composed of a display device 20, a processor 22, and amemory device 24. Alternatively, the display system may include acommunications link 26, a user input device 28, a display sensor 30 forsensing the luminance and/or color output of one or more light-emittingelements of the display device or a signal that is correlated with theluminance output of one or more light emitting elements and/or anambient sensor 32 for measuring the luminance and/or color of theambient lighting environment.

The display device 20 may be any projection or direct-view electronicdisplay device capable of providing four or more color primaries thatemit light within the visible spectrum wherein the spectral compositionof each of the at least four color primaries are unique from one anotherand are not a linear combination of one or more of the others. Displaydevices of this type have been described previously in the literatureand include digital projectors with increased color gamut, such as thosedescribed by U.S. Pat. No. 6,648,475 (Roddy et al.) and WO 01/95544(Ben-Chorin et al.), as well as digital projectors with increasedbrightness, such as described by U.S. Pat. No. 5,233,385 (Sampsell).Similarly appropriate display devices may also be direct-view displaydevices with increased color gamut as described by U.S. Pat. No.6,570,584 (Cok et al.), U.S. Patent Application 2002/0191130 (Liang etal.) and U.S. Patent Application 2004/0051724 (Brown Elliott et al.) orthey may be display devices with higher luminance efficiency such asdescribed in U.S. Ser. No. 10/812,787 (Miller et al.) filed on 29 Mar.2004. It is important to note that projection displays may present colorprimaries temporally sequentially or simultaneously, and eitherspatially patterned or fully-sampled. Direct-view displays typicallypresent color temporally simultaneously and spatially patterned. As willbe discussed more fully later, the color manipulations performed as partof this invention may result in spatial artifacts that may need to beconsidered if one is to employ this invention on a display withspatially patterned light-emitting elements.

The processor 22 may be any general purpose or specialized processorcapable of performing the calculations necessary for performing thesteps of this invention. The memory device 24 may include a programmableand/or fixed memory capable of storing any video information to bedisplayed, information relevant to the calibration of the displaydevice, a specification for the color distortions to be introduced, thename and/or address of the owner of the display system, and other suchinformation.

The optional communications link 26 may be used to communicate data tobe displayed, specifications for the color distortions and/or otherinformation such as copyright information to be rendered when performingthe color rendering. The optional user input device 28 may be used bythe user to input additional information that is to be encoded into theimage. The user input device 28 may also be used to alter the magnitudeof the difference between spatial regions in the event that theinformation that is rendered to produce the distortions become visibleduring viewing, for example due to a calibration error.

The optional display sensor 30 is a sensor that is used to sense theoutput of one or more of the color primaries or their combinations. Thedisplay sensor 30 will ideally perform radiometric or calorimetricmeasurements of the light output of the display device. The displaysensor 30 may alternatively measure a value correlated with the lightoutput of the display device such as the current or voltage drawn by thelight-emitting element within the display device in order to estimate aluminance output of the display device using a stored look-up table orother mathematical relationship.

The optional ambient sensor 32 may be used to measure the ambient lightthat is incident on or reflected by the display screen. Ideally thisdevice will measure the spectral radiance of the ambient light. However,in a controlled lighting environment, such as a motion-picture theatre,simpler devices such as a device that measures the intensity of theambient illuminant as well as estimating the type of light source canprovide adequate information if any ambient light sensor is necessary.Further, in viewing environments with fixed lighting, a sensor tomeasure ambient light will generally not be necessary. Further, undermany circumstances, ambient light will tend to reduce the contrast ofthe image produced by the display device which will tend to obscure anyvisible differences and therefore, such a sensor is not always required.

A preferred embodiment of this invention is shown in FIG. 3. As shown inthis figure, the display device 20 is characterized in step 40. Thischaracterization will provide a method of predicting the color andluminance of the light produced by the display device for each inputcode value and input code-value combination that the display is capableof producing in the range of illumination environments that are likelyto be applied. Although such a model can involve characterizing thedisplay's performance under a wide range of conditions, simpler modelsmay also be applied. One relatively complex characterization model is apair of N-D look-up tables where N represents the number of colorprimary channels, and D represents dimensions. The first, and mostimportant of these N-D lookup tables represents the color and luminanceoutput of the display device for all possible combinations of input codevalues. The second of the N-D lookup tables represents the reflectanceand spectral reflectivity of the image display surface for all possiblecombinations of input code values. Simpler models may also be utilized.One simplification is to assume that the display device will be used indarkened room conditions or that the reflectance of the image displaysurface will be inconsequential, making one of the N-D lookup tablesunnecessary. Alternately, one might assume that reflectivity isindependent of code value and therefore, the N-D lookup table may bereplaced by a simple one-dimensional look up table. A secondsimplification is to assume that the chromaticity and the luminance ofthe light produced by the display device are independent of one another.In this case, it is only necessary to determine a function relating codevalue to luminance for each of the color channels as well as tocharacterize the chromaticity coordinates of the color primariesemployed in the display device. One skilled in the art will recognizethe known variants of additive color system models that can be applied,depending on the system characteristics and the level of accuracyrequired.

Using this data as input and assuming that the image signal that will beinput to the display system has three color channels, a set ofconversion methods are produced in step 42 in order to map each of theincoming values to one of m possible sets of code values where one setof code value combinations will be applied to the majority of the scenedata and the remainder will provide the output code value combinationsto be applied to the selected regions that are to be rendered withdifferent primary combinations. Many methods for determining candidatecombinations of four or more output signals to represent the inputthree-channel color input signal may be developed. Assuming that thecolor and luminance of the display device are independent of oneanother, methods for determining possible mappings from a three-channelcolor input signal to an at least four-channel color output signal havebeen previously disclosed in co-pending commonly assigned U.S. Ser. No.10/607,374 (filed Jun. 26, 2003) and U.S. Ser. No. 10/812,787 (filedMar. 29, 2004) which are incorporated herein by reference. A methodsuited for this transformation is also provided in FIG. 4. Using theseapproaches allows the proportion of the luminance intensity of the gamutdefining primaries (2, 4, and 6) to alternative color subgamuts to beselected through what is known as a “mixing ratio”. Within the preferredembodiment, the majority of the scene will be rendered using a mixingratio in the neighborhood of 0.5 to provide maximum image quality.Alternative renderings may be formed using an alternative set ofsubgamuts and any mixing ratio value between 0 and 1.0 other than 0.5.

One alternative approach to producing in step 42 the conversion methodis to characterize the aim luminance and chromaticity values for eachinput code value combination; apply a model of the ambient illuminationto calculate the luminance and chromaticity coordinates of the lightreflected from the display for all possible code value combinations; addthe reflected luminance value to the output luminance for all code-valuecombinations to determine the system luminance in the ambientenvironment; and determine the chromaticity coordinates of each primaryin the ambient environment by computing the weighted average of thechromaticity coordinates of the emitted and reflected display luminancewhere the weighting factors are proportional to the total luminanceattributable to display output and reflected luminance. The resultingrelationship between code values and the luminance and chromaticityvalues computed here provide the information necessary to transform theinput three-color signal to intensities and chromaticity coordinatesnecessary for application in this method. Characterization of the aimluminance and chromaticity values can be performed in real-time toaccount for less than optimal display performance caused by the displaysystem's drift or decay. Having this final N-D lookup table, this tableas well as the aim luminance and chromaticity values are transformed toa perceptually uniform color space such as CIELAB and the m possiblesolutions for each value in the input N-D lookup table with the minimumdifference from the aim value are selected. The corresponding codevalues for the resulting m possible solutions are then used to populatethe m N-D lookup tables. While this process can be relatively timeconsuming, it needs only to be computed once for as long as theluminance output of the display and the ambient illumination areconstant. In simpler implementations such as those described in theco-pending applications and the one shown in FIG. 4, it is also possibleto embed this step as a set of real-time calculations that are performedfor each input code value combination in place of the look-up function.Using this method, a set of 3×3 matrices is formed together with a setof decision rules for selecting a set of one or more 3×3 matrices andthese serve as the conversion method in step 42, the application ofwhich is shown in FIG. 5.

The input image data to be rendered is then acquired in step 44. Nextthe specification for the embedded watermark is acquired in step 46.This specification will provide a description of the spatial, temporal,and or color characteristics of the watermark. The system theninterprets in step 48 this specification and determines in step 50 thetype(s) of visibly undetectable color distortions to embed. If thespecification provides a list of colors that are to be rendereddifferently than the remainder of the image is rendered, the colors inthe input image that are within specified bounds of these colors arethen selected and their spatial position is determined in step 52. Ifthere is any spatial description provided directly from thespecification or converted from color information, the system renders instep 54 any spatial description into a binary or integer image. Thisbinary or integer image represents which of the m N-D look up tables areto be indexed for each spatial location in the image. Alternatively, thespatial description image produced in 54 need not be restricted tointeger values, implying fractional linear combinations of any of the mN-D look up table solutions. Such a non-integer image may or may not beencoded in a quantized, integer-based format. It should be noted that ifno color or spatial information is provided, then a uniform image isgenerated with all pixels in the image having the same index to one ofthe m conversion methods. This spatial information is then applied instep 56 to the input image data by applying the correct combination of3×3 matrices as indicated by the binary or integer image and thelocation of the color in color space. This step will be furtherexplained when discussing FIG. 6. The image is then output in step 58 tothe display device 20 if the image is rendered in real time or output tothe memory 24 if the image is being preprocessed for display at a latertime. A test is performed in step 60 to determine if all image renderingis complete. If it is complete, the process is complete in step 62. Ifnot, any specified time sequence is used to update in step 64 thespatial map by replacing any values in the spatial map according to thetime sequence. Once the spatial image is updated, it is applied in step56 to the image data for the next frame of video and the steps 56, 58,60 and 64 are repeated until all of the image data has been rendered. Byperforming the steps 40 through 64, the rendering process is completedand the images are rendered with the embedded invisible colordistortions that await detection by an image-recording device.

As mentioned earlier, a method suited for transforming an incomingthree-channel color signal to a four or more channel color signal (e.g.,generating the conversion method) is provided in FIG. 4 and describedhere. The CIE chromaticity coordinates are input in step 70 for eachcolor primary. Phosphor matrices, describing the CIE tristimulus valuesfor color stimuli produced by the additive combination of three colorprimaries, are then calculated in step 72 for all subgamuts to be usedin the color conversion using methods well known to those skilled in theart. The primaries are then sequentially arranged in step 74 from theprimary with the most short wavelength energy to the primary with themost long wavelength energy. This may be done using the chromaticitycoordinates such that the primaries are arranged to follow the border ofthe chromaticity diagram's spectrum locus from blue to red and back toblue again. All of the subgamuts that may be formed from neighboringsets of three primaries are then determined in step 76. Each of thesesubgamuts will then be defined by three primaries with a center primaryfrom the arranged in step 74 list and two neighboring primaries at theextremes or ends of the triangle used to form the subgamut. As anexample, we will assume a display device having the four primaries shownin FIG. 1. For such a device the primaries would be arranged in a listprogressing in the order blue 6, cyan 10, green 4 and red 8. In such adevice a first subgamut triangle may be formed from blue 6, cyan 10 andgreen 4 primaries and would have the cyan primary 10 as the centerprimary and the blue 6 and green 4 primaries as the neighboring endprimaries. A second subgamut would be defined with the green primary 4as the center primary and the cyan 10 and red 2 primaries as theneighboring end primaries. The final subgamut that can be created fromneighboring primaries would be formed with the red primary 2 as thecenter primary and the green 4 and blue 6 primaries as the neighboringend primaries.

For each of the subgamuts determined in step 76, the theoreticalintensities for forming each primary that is not in each subgamut arecalculated in step 78 (e.g., for the subgamut formed from the blue 6,cyan 10 and green 4 primaries the theoretical intensities are calculatedfor forming the red primary). These calculated intensities have valuesless than zero, as it is not physically possible to form these colorsusing these subgamuts. However, this calculation is useful as the ratiosof the intensities for the outside primaries in the gamut define a linethat segments subgamuts within the color space. The ratio of thetheoretical intensities of the two primaries that are at the ends of thecurrent subgamut used to form each primary outside the current subgamutis then calculated in step 80. All other subgamuts are then determinedin step 82 by forming subgamuts where first one and if possible moreprimaries in the ordered list are omitted as one progresses through thelist, keeping in mind that to form a subgamut requires three primaries.As it will be possible to form each color using multiple subgamuts,other input selection criteria may be input in step 84 which can be usedto define the decision rules around the default rendering values and them alternative sets of rendering values. Finally, a set of decision rulesis determined in step 86. The decision rules are formed knowing that anycolor having all-positive color-primary intensities when formed from oneof the subgamuts determined in step 76 lies within that subgamut. Anycolor having one or more negative primary values lies outside thesubgamut. However, any color having a ratio that is larger than theratio determined in step 80 will lie to the same side of a line as theend primary that is used in the numerator of the ratio calculation wherethe line intercepts the center primary and the corresponding primaryfrom outside of the subgamut. These decision rules will also considerother information such as a preferred set of primaries for the currentof the m renderings. Other information such as power consumption orlifetime of the primaries, or predictions of overall image quality tohelp provide a selection of a default combination of subgamuts, as wellas one or more alternative combinations of subgamuts to be employed inrendering may also be considered.

Based upon this information, a set of logic may be formed that indicatesall possible home subgamuts for any input color which may be definedfrom a set of n primaries by calculating n−2 sets of intensity valuesand n/2 comparisons as opposed to calculating the intensities for alln!/(3!*(n−3)! combinations of the n primaries. Steps 70 through steps 82are dependent upon the chromaticity coordinates of the primaries and forthis reason, need only be performed once. These steps may be performedat device startup but may also be performed once during manufacturing orinitial startup of the display device and the resulting decision rulesstored in memory, allowing each of the following steps to be performedwithout further delay.

FIG. 5 shows a method for applying in step 56 the input image conversionusing the method of the preferred embodiment. To apply this method, theCIE XYZ tristimulus values corresponding to each incoming code value areinput in step 88. Next the decision rules and 3×3 matrices determinedusing the method shown in FIG. 4 are input in step 89. The color-primaryintensities and ratios for each set of XYZ values are then calculated instep 90 for each of the non-overlapping and neighboring subgamutsdetermined in step 76 of FIG. 4. Based upon the decision rules formed instep 86 of FIG. 4, all subgamuts useful in creating the desired colorare determined in step 92. The appropriate subgamut or subgamuts arethen selected in step 94 based on the rendering information for thecurrent of the m renderings and the decision rules determined in step86.

Using this method for the color conversion, the current of the mthrenderings are then determined by calculating in step 96 the intensitiesfor each subgamut. A weighted average of the intensities are thencalculated in step 98. Generally, the weightings in this average will bethe mixing ratio for each subgamut. This weighted average produces therelative luminance intensity for each primary. These relative luminanceintensities are then converted in step 100 to code values using thecharacterization data obtained in step 40 of FIG. 3 and these codevalues compose the output image discussed in FIG. 3. It should be notedthat not only does this method for piracy protection provide thisfeature but it also can have the benefit of increasing the color gamutvolume of images produced by the display device. The color gamut volumerefers to a three-dimensional volume of achievable luminance andchrominance values for color stimuli produced by the display device.Whenever an additional primary is outside the color gamut triangle shownin FIG. 1, this fact is relatively obvious. What may not be quite soobvious from the earlier discussion is that for additional colorprimaries whose chromaticities are on or inside the color gamut boundary8, colors within the color gamut of the display device can be formedusing more than one set of three of the primaries and still provide anopportunity for color mixing as was described for the additional colorprimaries outside the color gamut boundary 8. Even under theseconditions, the color gamut volume can be increased, because colors nearthis primary may be produced with higher luminance than could beproduced without this additional primary.

It was noted earlier that if the image-forming mechanism of the displaydevice is comprised of a pattern of spatially separate light emittingelements of different colors, it is necessary to impose additionalconstraints to enable the method of this invention. In fact, such adisplay serves to place an additional constraint on the selection ofcandidate mixing ratios. This constraint arises from the fact that whena significant amount of the energy is shifted from one light emittingelement to a neighboring light emitting element, a distinct spatialpattern may become visible in the display image that would make anyspatial pattern visible even if the integrated color output from each ofthe light-emitting elements in a pixel for two different solutionsprovided exactly the same chromaticity and luminance values. One way toavoid such a pattern is to employ only temporal variations, avoidingrendering a spatial information pattern as an invisible colordistortion. Another method is to constrain the amount of luminance thatcan be moved from one light-emitting element to another such that achange in the spatial appearance of the pixel is not visible. To addthis constraint, the pixel pattern may be analyzed when each candidatecolor rendering is applied using a visual difference model such as theone described by Zhang and Wandell in the 1997 SID Journal entitled “Aspatial extension of CIELAB for digital color image reproduction” todetermine if the spatial pattern produced with each rendering method isvisually distinct. If the two pixel patterns are visually distinct fromone another, this candidate color rendering is discarded. Otherwise, thecandidate color rendering should provide an invisible color distortion.

Since it may not be intuitive that a pair of displayed colors thatappear indistinguishable when viewed by the unaided human eye can beformed from two different combinations of four or more primaries and yetreproduce inconsistently or non-uniformly when recorded using a typicalimage-capture device and viewed on another or the same display device,an example is provided here. In order to provide this example, it isnecessary to recognize that the CIE 1931 color-matching functions werederived from color-matching experiments in which human observers wereasked to select visually matched color stimuli that had differentspectral compositions. Therefore it is assumed and has been shown thatcolor stimuli of differing spectral compositions but having equivalentXYZ tristimulus values computed using the CIE 1931 color-matchingfunctions will produce the same perceived color when viewed underequivalent viewing conditions. XYZ tristimulus values may be convertedto chromaticity coordinates via known methods. Therefore, colors whosechromaticity coordinates and luminance values match will be perceptuallyindistinguishable to a viewer with normal color vision when viewed underequivalent conditions. However, this visual match may not be achievedunder all viewing conditions, particularly in dim viewing conditionswhere the retinal rods may play a role in color perception, requiring adifferent color space to have this same property in the strictest sense.Additionally, normal variation among viewers may result in varyingdegrees of color difference to each individual. Despite thispossibility, the 1931 CIE chromaticity space provides an adequatedescription across a broad range of viewing conditions. It should beclear to one skilled in the art that this same invention can be appliedwhile employing a different color-matching function set or colorspecification paradigm, perhaps more appropriate for a given viewingenvironment or viewer population.

Having a color space in which it can be determined if color stimuli withdifferent spectral compositions are perceptually equivalent, it is thennecessary to demonstrate that there are at least two possible solutionsfor combining the output of four or more color primaries to producestimuli having equivalent chromaticity coordinates and luminance andthat these at least two solutions would be recorded differently by adigital image-capture device with representative spectral sensitivities.To perform this analysis we will assume a display with primaries havingnarrow-band emission, as may be characteristic of LED sources. FIG. 6shows the spectral power distribution for four color primaries havingnarrow-band emission that may be characteristic of red 102, green 104,blue 106, and cyan 108 color primaries. These spectral powerdistributions can be integrated appropriately using calorimetriccomputations known to those skilled in the art to determine the 1931 CIEx,y chromaticity coordinates for each of these primaries. These data areshown in Table 1. TABLE 1 Primary x y red 0.7073 0.2927 green 0.23050.7531 blue 0.0469 0.2936 cyan 0.1564 0.0179

We will further select an image-capture system. The spectral sensitivityof this capture system is shown in FIG. 7 and represents typical videocamera spectral sensitivities as published by Giorgianni and Madden inDigital Color Management: Encoding Solutions, Addison-Wesley, 1998. Asshown in this figure, the capture system is sensitive to bands of energyin the red 110, green 112 and blue 114 regions of the spectrum. Thecamera processes the data it receives, first performing a white balancecorrection by scaling the red, green, and blue image-capture signalsindependently such that a known or theoretical scene white producesequal signals in each color channel. Here a simple white-balance isemployed that scales its responses to unity for the brightest object inthe scene. Other variations are possible and likely, which would changethe relative values in the present example, but have no effect on theusefulness of the present invention. The balanced signals are renderedthrough a grayscale 116 as shown in FIG. 8, which provides a correctionfor viewing flare and adds a visually pleasing contrast boost. Finally,the grayscale-rendered color signals are rotated with a 3×3 matrix toapproximate CIE XYZ tristimulus values for display. Skilled readers willnote that a practical camera system would include the encoding of thesereproduction displayed CIE XYZ tristimulus values in a standard metricsuch as sRGB or YCC. For the purpose of this example, this step isomitted because it would be inverted upon subsequent display with anaccurately calibrated display system. The reproduction displayed CIE XYZtristimulus values, possibly expressed in a color representation such asCIELAB, are the quantities of interest.

To further specify this example, we select a set of colors to displaywith the specified four-color display system. The colors selected forthis example are a subset of the colors specified for the Macbeth ColorChecker Color Rendition Chart, published by Macbeth, Baltimore, Md.,illuminated by CIE Standard Illuminant D65. The selected patchesrepresent dark skin, light skin, foliage, bluish green, orange, moderatered, yellow-green, orange-yellow, green, red, yellow, white, fourdensities of gray and black. We select the foliage patch to providespecific illustration of the example. The foliage patch under D65illumination has CIE XYZ tristimulus values of 11.42, 15.01, and 7.42,relative to a perfect white with 100 units of luminance value Y. Usingthe red, green, and blue (RGB) display primaries from Table 1, 2.613,12.25, and 0.1549 units of luminance are required, respectively, toproduce a stimulus having the same CIE XYZ tristimulus values relativeto a perfect white with 100 units each of the red, green, and blueprimaries. Likewise, using the red, green, and cyan (RGC) displayprimaries from Table 1, 3.456, 8.339, and 3.220 units of luminance arerequired. Because the color stimuli produced by the RGB primaries andthe RGC primaries have identical CIE XYZ tristimulus values, they willappear identical in color under the same viewing conditions to anobserver with normal color vision. However, when recorded andredisplayed by the specified image capture system, the results willdiffer. The foliage patch displayed with RGB primaries results in cameraresponses of 0.0772, 0.1033, 0.0405, when white balanced to unityresponse values to the assumed brightest stimulus, the displayed RGCwhite. The camera responses resulting from the same foliage color asdisplayed with RGC primaries are 0.1020, 0.1269, 0.0667. In order torelate these differences on a perceptual scale, it is important to lookat the colors reproduced from the image-capture system signals. TheCIELAB L*,a*,b* values of the reproduced RGB foliage patch are 30.42,−18.22, and 27.77, while those of the reproduced RGC foliage patch are35.01, −14.94, and 21.15. The difference in color, or delta E*, theEuclidean distance, between these two three-dimensional points is 8.7.Since a delta E* difference of 1.0 is visible to most observers, thisdifference would be clearly visible. Table 2 shows the reproduced CIELABvalues for all 17 of the example colors using the RGB and RGC displayprimaries, as well as the resultant delta E* differences between them.TABLE 2 Reproduction from Reproduction from Patch capture of RGB captureof RGC Delta Description L* a* b* L* a* b* E* Dark Skin 24.34 13.0818.68 29.49 11.54 13.55 7.42 Light Skin 53.05 16.75 22.67 61.64 14.8415.9 11.1 Foliage 30.42 −18.22 27.77 35.01 −14.94 21.15 8.7 Bluish Green53.54 −35.47 −0.52 67.43 −22.7 −2.48 18.97 Orange 50.03 32.23 68.3951.86 30.9 59.79 8.9 Moderate Red 39.07 42.06 22.95 45.29 37.09 16.4610.28 Yellow Green 57.97 −24.47 64.77 61.21 −22.31 53.85 11.59 OrangeYellow 58.58 15.09 71.53 61.07 14.35 61.17 10.68 Green 37.63 −37.7 34.3942.17 −31.47 26.49 11.04 Red 31.07 46.99 35.59 34.01 44.1 28.52 8.18Yellow 68.52 0.62 87.61 70.67 0.61 76.11 11.7 White 74.5 −3.58 0.5591.47 −0.36 −2.01 17.46 Gray 1 64.31 −2.78 0.17 79.74 0.02 −2.07 15.85Gray 2 49.6 −2.67 0.07 62.74 −0.19 −1.8 13.5 Gray 3 33.93 −2.3 −0.5744.78 −0.21 −1.93 11.14 Gray 4 17.85 −1.56 −1.07 26.37 0.01 −1.95 8.72Black 3.61 −0.39 −0.6 8.3 0.25 −1.64 4.84

These delta E* differences which range from 7.42 to as much as 18.97,all of which would undoubtedly be visible, and likely be objectionable,to a viewer of the captured image. This example demonstrates thatvisually matched color stimuli on a display system of the presentinvention will become visibly distinct when reproduced from a typicalimage-capture device, illustrating the value in the present invention indistorting unauthorized reproductions.

While the invention has been described with particular reference to itsapplication in protection of copyrighted material and in particular tomotion picture films, it will be recognized that this technology may beapplied in other domains as well. In another embodiment, the displaysystem may be embedded in a portable display device and used to displayinformation such as the name of the owner of the display system and/orhis or her address in order to deter theft or aid the return of lostitems. In another embodiment, the display system may be embedded in achild's toy to enable the hidden display of information that can berevealed using a camera or other specialized viewing device. Such aviewing device may consist of low-cost items such as color filters toimprove the visibility one or more of the four or more light emittingelements.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   2 red primary chromaticity coordinates-   4 green primary chromaticity coordinates-   6 blue primary chromaticity coordinates-   8 color gamut boundary-   10 cyan primary chromaticity coordinates-   20 display device-   22 processor-   24 memory device-   26 communications link-   28 user input device-   30 display sensor-   32 ambient sensor-   34 ambient lighting environment-   40 characterize display device step-   42 produce conversion methods step-   44 acquire input image data step-   46 acquire specification step-   48 interpret step-   50 determine type(s) step-   52 determine spatial position step-   54 render spatial description step-   56 apply spatial information step-   58 output image step-   60 test complete step-   62 complete step-   64 update spatial map step-   70 input chromaticity coordinates step-   72 calculate phosphor matrix step-   74 arrange primaries step-   76 determine subgamuts step-   78 calculate theoretical intensities step-   80 calculate ratio step-   82 determine subgamuts step-   84 input selection criteria step-   86 determine decision rules step-   88 input XYZ values step-   89 input decision rules and matrices step-   90 calculate intensities and ratios step-   92 determine subgamuts step-   94 select subgamuts and phosphor matrices step-   96 calculate intensities step-   98 calculate weighted average of intensities step-   100 convert intensities to code value step-   102 spectral power distribution for red primary-   104 spectral power distribution for green primary-   106 spectral power distribution for blue primary-   108 spectral power distribution for cyan primary-   110 camera red sensitivity-   112 camera green sensitivity-   114 camera blue sensitivity-   116 camera grayscale

1. A color display system, comprising: (a) a display device having fouror more visible color primaries capable of producing metamericallymatched color stimuli; and (b) a processor for controlling the four ormore color primaries to selectively render portions of an image or imagesequence such that visually equivalent colors displayed in two or moreimage portions differ in their spectral composition.
 2. The colordisplay system claimed in claim 1, wherein the four or more colorprimaries are arranged in a spatial pattern and wherein the differentportions of the image or image sequence are rendered such that there isno perceived difference in the spatial pattern of the input image colorwhen displayed in the two or more portions.
 3. The color display systemclaimed in claim 1, wherein the portions contain watermark informationand/or color degradation when captured with an image-capture device andsubsequently redisplayed.
 4. The color display system claimed in claim1, wherein the processor converts three or more channel color-imagesignals to four or more channel color-image signals for use by thedisplay device.
 5. The color display system claimed in claim 1, whereinan input image color displayed in a first portion is rendered using onecombination of the four or more color primaries and a given input imagecolor displayed in a second portion is rendered using a secondcombination of the four or more visible color primaries.
 6. The colordisplay system claimed in claim 1, wherein an input image is renderedfor display using the four or more color primaries in real time.
 7. Thecolor display system claimed in claim 1, wherein an input image ispre-rendered for display using the four or more color primaries forsubsequent display.
 8. The color display system claimed in claim 3,wherein the processor receives a three or more color input image signal,and an instruction for spatial, temporal and/or color patterning fordifferent portions of an image when embedding the watermark informationand/or causing the significant color degradation when captured with animage capture device and subsequently redisplayed.
 9. The color displaysystem claimed in claim 8, wherein at least one of the image portionshas a shape of a text character.
 10. The color display system claimed inclaim 9, wherein one or more regions provides textual information,wherein the textual information is selected from the group consistingof: (a) a name of the copyright owner; (b) a date of the copyright; (c)an owner of the color display system; (d) an address of the owner of thecolor display system; (e) a location of the color display system; and(f) a reminder of copyright penalties.
 11. The color display systemclaimed in claim 8, wherein the instruction of the spatial and/ortemporal pattern includes a random variable to decrease predictabilityof the embedded watermark information and/or the significant colordegradation when captured with the image capture device and issubsequently redisplayed.
 12. The color display system claimed in claim8, wherein the instruction of the color pattern includes colors that areparticularly salient in human memory.
 13. The color display systemclaimed in claim 12, wherein the instruction of the color patternincludes colors often associated with skin, sky, and/or foliage.
 14. Thecolor display system as claimed in claim 1, wherein the color displaysystem is distributed with a dedicated viewing apparatus.
 15. The colordisplay system as claimed in claim 14, wherein the dedicated viewingapparatus contains a color filter.
 16. The color display system asclaimed in claim 1, wherein a color primary is rendered to image pixelsin a particular color cluster different from color primary renderingapplied to remaining pixels in a scene.
 17. The color display system asclaimed in claim 1, wherein the display device is a projection displaydevice.
 18. The color display system as claimed in claim 1, wherein thedisplay device is a direct view display.
 19. The color display system asclaimed in claim 1, further comprising: c) a display sensor formeasuring a value that correlates with light output of one or more ofthe four or more visible color primaries.
 20. The color display systemas claimed in claim 19, wherein the display sensor measurescharacteristics of the display device selected from the group consistingof tristimulus values, chromaticity coordinates, luminance, radiance,and reflectance.
 21. The color display system as claimed in claim 19,wherein the display sensor measures current and/or voltage of a lightsource within the display device.
 22. The color display system asclaimed in claim 21, wherein a measurement of current and/or voltage isused to compute and/or derive an output luminance value.
 23. The colordisplay system as claimed in claim 19, wherein the processor uses thevalue measured by the display sensor to dynamically alter the spectralcomposition of one or more of the portions of the image or imagesequence.
 24. The color display system as claimed in claim 19, whereinthe processor provides real time characterization of the four or morevisible color primaries.
 25. A method for rendering different portionsof an image or image sequence such that a given input image colordisplayed in two or more portions has different spectral composition andis perceived as visually equivalent, comprising the steps of: (a)selecting two or more subgamuts that enclose the color coordinatesassociated with the input image color; wherein each subgamut is definedby the color coordinates of three color primaries; (b) calculatingintensities of each of the three color primaries within each subgamut;(c) calculating two or more weighted averages of the calculatedintensities; and (d) converting the calculated intensities to codevalues for displaying an image.
 26. A method for using visible light todeter unwanted copying of image content, comprising the steps of; (a)combining four or more visible color primaries to render differentportions of an image or image sequence such that a given input imagecolor displayed in two or more portions has a different spectralcomposition and is perceived as visually equivalent; and (b) displayingthe image portions as part of the image content.
 27. The method claimedin claim 26, wherein the two or more portions form watermark informationand/or undergoes significant color degradation when captured with animage capture device and is subsequently redisplayed.
 28. The methodclaimed in claim 26, wherein at least one of the portions has the shapeof a text character.
 29. The method claimed in claim 28, wherein one ormore regions are shaped to provide textual information, wherein thetextual information is selected from the group consisting of: (a) a nameof the copyright owner; (b) a date of the copyright; (c) an owner of thecolor display system; (d) an address of the owner of the color displaysystem; (e) a location of the color display system; and (f) a reminderof copyright penalties.
 30. The method claimed in claim 26, furthercomprising the steps of: (c) receiving three or more color input imagesignals, and an instruction for spatial, temporal and/or colorpatterning for the two or more portions of an image; and d) partitioningthe three or more color input image signal into different portionsaccording to the instruction.
 31. The method claimed in claim 30,wherein the instruction of the spatial and/or the location of thetemporal pattern include a random variable to decrease predictability ofa position and/or rendering of at least one of the two or more portions.32. The method claimed in claim 30, wherein the instruction of the colorpattern includes colors that are particularly salient in human memory.33. The method claimed in claim 26, wherein a timing or location of atleast one of the two or more portions is determined as a function of arandom variable.
 34. A display device, comprising: (a) four or morecolor primaries that emit visible light; and (b) a means for combiningthe four or more visible color primaries to produce two or more regionsof color that are visually equivalent and have different spectralcomposition.
 35. The display device claimed in claim 36, wherein thedisplay device uses sequential color presentation to form an image. 36.The display device claimed in claim 34, wherein the display devicedisplays a spatial pattern of color primaries to form an image.
 37. Amethod for hiding and revealing text or image data using a displaydevice, comprising the steps of: (a) combining four or more visiblecolor primaries to render portions of an image or image sequence suchthat visually equivalent colors displayed in two or more image portionsdiffer in their spectral composition; and (b) providing a means forvisually differentiating the portions.
 38. The method claimed in claim37, wherein the means for visually differentiating the portions is adedicated viewing apparatus.
 39. The method claimed in claim 38, whereinthe dedicated viewing apparatus uses color filters.
 40. The methodclaimed in claim 38, wherein the dedicated viewing apparatus is acamera.
 41. The method claimed in claim 26 wherein a color primary isrendered to image pixels in a particular color cluster different fromcolor primary rendering applied to remaining pixels in a scene.
 42. Themethod claim in claim 37, wherein a color primary is rendered to imagepixels in a particular color cluster different from color primaryrendering applied to remaining pixels in a scene.
 43. The color displaysystem as claimed in claim 1, wherein three of the four or more visiblecolor primaries emit red, green, and blue light.
 44. The color displaysystem as claimed in claim 1, wherein light emitted by at least one ofthe four or more visible color primaries is either white, cyan, yellow,or magenta.
 45. The color display system as claimed in claim 1, furthercomprising: (a) a first visible color primary having a firstchromaticity coordinate; (b) a second visible color primary having asecond chromaticity coordinate; and (c) wherein the first and secondchromaticity coordinates are substantially the same and spectracorresponding to the first and second visible color primaries aresubstantially different.